The proposed project involves the use of low energy (1 keV-10 keV) beams of Ar+, Xe+, or N2+ to study the structures of human adenovirus type 2 (adenovirus 2) and equine herpes virus type 1 (EHV-1). The experimental strategy is to employ ion beams with limited (5.0nm-15.0nm) penetrating power to etch or erode the virus surface progressively from the outside toward the center of the particle. At various stages of the etching process irradiated virions will be examined in the electron microscope to assess the extent of erosion. Preliminary experiments have shown clearly that as outer layers of the virus are eroded away, internal components become visible in shadowed preparations. The results of electron microscopic analyses will be correlated with biochemical studies, involving SDS-polyacrylamide gel electrophoresis, to determine the effects of etching on specific viral polypeptides. This correlation should allow one to identify the protein components of viral structures revealed after different amounts of etching. Similarly, the DNA component of etched virions will be examined, by agarose gel electrophoresis, to identify regions of the viral DNA closest to the particle surface. This overall analysis will clarify the structure of the adenovirus 2 core and provide definitive information about the location of viral proteins V and VI. Ion etching of EHV-1 should reveal the structure of the tegument layer and its polypeptide composition. Analysis of EHV-1 nucleocapsids should clarify the arrangement of DNA in these structures and allow one to determine the polypeptide composition of the core found in the center of the DNA-containing torroid.